We all know movies that butcher a great work of literature. There are also many examples of excellent movies that are based on pretty mediocre books or short stories.
More of a niche are movies based on great literature, where the director has decided to go a different direction tonally or thematically, but still made a great book (albeit one that is unfaithful to the book).
Examples of this are, the Thing Red Line by Terrence Mallick, which is based on James Jones novel of the same name. The book is violent and visceral while the movie is also very violent but the movie dwells on some of the characters' spiritual side.
Another example is Barry Lyndon. the book is essentially a comedy - BL is an unreliable narrator who we laugh at. He is a deeply unpleasant character, although he believes himself always right and highly honourable. His Irishness is mocked as are his pretentions to artistocratic blood(Thakeray felt that Irish people used duelling to get their way too much). The book is a masterpiece - IMHO Thakeray's greatest. The movie has the same character but he's sympathetic and the tone is somber and tragic. But although it's tonally unlike the book and although BL's character is changed; the movie is still a masterpiece.
Can you think of other examples where the director takes a classic, makes a totally different story, but a great story nonetheless.